Short answers, pulled from the story.
The Tuscan order is one of the two classical orders developed by the Romans, alongside the composite order. It features unfluted columns, a circular base, and a simplified entablature with no triglyphs or guttae, making it the plainest of the five orders named during the Renaissance.
The Tuscan order was first classified as a separate formal order by Isidore of Seville in the sixth century, in his work the Etymologiae. It was further refined and codified during the Italian Renaissance, notably by Sebastiano Serlio in his Regole generali di architettura of 1537.
Most authorities, including Vitruvius, Vignola in his Cinque ordini d'architettura of 1562, and Palladio in his I quattro libri dell'architettura of 1570, give the Tuscan column a proportion of 1:7. Serlio alone prescribed a stockier ratio of 1:6.
Serlio described the Tuscan order as suitable for fortified places, including city gates, fortresses, castles, treasuries, prisons, and seaports. Palladio associated it with villa barns, large amphitheatres, and as a ground-floor order in multi-storey buildings.
According to an account recorded by Horace Walpole, Lord Bedford gave Jones a very low budget and asked for a simple church "not much better than a barn." Jones replied that Bedford would then have "the handsomest barn in England." The church, completed in 1633, became a notable example of the Tuscan order applied to a religious building.
Because the Tuscan mode can be worked up by a carpenter with basic planing tools, it became part of the vernacular Georgian style. It was widely used in New England and Ohio well into the nineteenth century, and in garden design it appears in gate posts and fences as a form sometimes called "carpenter's Doric."